In recent years, according to progress of development of an electric vehicle and the like, vehicle structures have been desired to achieve further weight reduction in order to improve fuel consumption, and use of resin materials, instead of metallic materials represented by conventional iron material, has been studied. In particular, a fiber-reinforced resin material has been studied to use various fields, as an alternative material of metallic materials, due to light weight and excellent strength thereof.
When a bending load-carrying member such as a side face frame structure of vehicle skeleton is manufactured by using the fiber-reinforced resin material, a hollow structure is generally adopted in order to achieving both desired performance index (for example, strength, rigidity, energy absorption property, and the like) and weight reduction. For example, Patent Document 1 discloses an energy absorption vehicular component having a hollow structure and obtained by using a fiber-reinforced resin material. Such a conventional hollow structure body generally has the same thickness or shape of each shaped product.